1. Field of the Invention
The present invention relates to a sewing machine which is provided with Y-direction drive mechanisms for moving a drive frame for tensing and holding a cloth to be worked, on the table of the sewing machine in the back and forth directions of the sewing machine.
2. Description of the Related Art
FIG. 8 shows a conventional sewing machine 50 which is provided with Y-direction drive mechanisms. This sewing machine 50 is provided for stitching both a cylindrical cloth and a flat cloth and is constructed to include: a lower frame 51 extending in a direction X (i.e., in the right-and-left directions of the sewing machine 50) and supported generally horizontally; a table 52 supported generally horizontally on said lower frame 51; an upper frame 53 erected over said table 52 and in parallel with the lower frame 51; a pair of machine heads 54 arrayed in the direction X in front of said upper frame 53; a pair of beds 55 arrayed on the lower frame 51 in such a manner to correspond to the individual machine heads 54 as to have upper faces generally flush with the upper face of the table 52; a drive frame 56 placed on the table 52; a pair of Y-direction drive mechanisms 57 for moving said drive frame 56 on the table 52 in a direction Y; and an X-direction drive mechanism 58 for moving the same in the direction X.
The bed 55 is provided with a base portion 55a supported on the lower frame, and a cylindrical portion 55b extending forward from said base portion 55a. The table 52 is composed of a stationary portion 52a arranged from the back side to the left and right side portions of the sewing machine 50, and a lift portion 52b arranged in a front side recess of said stationary portion 52a. The lift portion 52b can be moved downward from the bed 55 so that the flat cloth and the cylindrical cloth can be worked, respectively, in the states where the lift portion 52b is moved upward and downward.
The Y-direction drive mechanisms 57 are so disposed below the stationary portion 52a on the left and right sides of the lift portion 52b, respectively, that they may not interfere with the vertically moving lift portion 52b of the table 52. The both Y-direction drive mechanisms 57 are individually jointed through slits 52c, which are formed through the table 52 to extend in the direction Y, to the end portions of a root portion 59 of the drive frame 56, as extending in the right-and-left directions of the sewing machine 50. The root portion 59 has the X-direction drive mechanism 58 for driving a frame portion 60 of the drive frame 56 in the right-and-left directions of the sewing machine 50.
If the number of the machine heads 54 is increased, however, the distance between the two Y-direction drive mechanisms 57 is enlarged so that the root portion 59 of the drive frame 56 is liable to deflect at its central portion 59a when the Y-direction drive mechanisms 57 are actuated. When the drive frame 56 is driven in the direction Y, therefore, the central portion 59a of the root portion 59 seriously vibrates to raise a problem that the positioning accuracy of the drive frame 56 is lowered.